1. Field of the Invention
The present invention relates to a power transfer device for an inboard/outboard motor.
2. Description of the Prior Art
Disclosed in Japanese Patent Laid-open Publication No. 4(1992)-143195 is a power transfer device for an inboard/outboard motor which includes a propeller unit mounted on the hull of a boat. The propeller unit comprises an input shaft for drive connection to the motor, an intermediate shaft in drive connection to a propeller shaft, a driven gear fixed to one end of the intermediate shaft and meshed with a pair of forward and backward gears rotatably assembled with the input shaft, and a pair of hydraulic clutches disposed between the input shaft and the forward gear and between the input shaft and the backward gear for selectively connecting the forward or backward gear to the input shaft.
When the power transfer device is shifted for forward drive, either one of the hydraulic clutches is engaged to drivingly connect the forward gear to the input shaft. While the other hydraulic clutch is maintained in a disengaged condition to permit free rotation of the backward gear on the input shaft. When the power transfer device is shifted for backward drive, the latter hydraulic clutch is engaged to drivingly connect the backward gear to the input shaft, while the former hydraulic clutch is disengaged to permit free rotation of the forward gear on the input shaft. Thus, the power transfer device is smoothly shifted for forward or backward drive. In the power transfer device, however, there occurs drag torque between the input shaft and the forward or backward gear when either one of the hydraulic clutches is maintained in a disengaged condition. This causes drag torque at the hydraulic clutch in a disengaged condition, resulting in loss of the drive torque and deterioration of the power transfer efficiency. As the drive torque is transmitted to the intermediate shaft from the input shaft through either one of the hydraulic clutches in each operation. It is required to provide the hydraulic clutches respectively in a large size for transmission of the drive torque. For this reason, the whole construction of the power transfer device becomes large in size.